You can also easily go to the border between Chile and Bolivia (5 hours from La Paz by bus / car) to climb Parinacota (6342m / F) + Pomerape (6282m / F) right beside to each other, and a bit further away Sajama (6542m / PD) the highest mountain in Bolivia.

3/ As far as weather is concerned, it's good for both. By the Chilean border it may be more stable as this area is quite dry in general.

I would reconsider Peru (it is only one 8 h from Lima to Huaraz). The trip is usually done overnight so you do no waste any days. I think seen the cordillera blanca and climbing there would be worth it.

The weather is definitely better in Bolivia, but Ecuador may be your best bet. Cotopaxi has the best weather of any peak in Ecuador, so if you end up there, focus on Cotopaxi and you can probably get it done. Iliniza Sur is good, but I had a lot of bad weather there and had to go back a second time later in my trip and we still ended up forcing it in bad weather. But you can get up Norte in almost any conditions, so it wouldn't be a totally wasted trip and you'd at least get some acclimatization before going for Cotopaxi. Quito is definitely more comfortable than La Paz for someone just arriving from the US as well. As for Bolivia, I don't think that you could do P. Alpamayo and H. Potosi in just 9-10 days. You need at least 3 nights in La Paz before you should even think about heading out into the mountains. Then a day to hike to BC for P. Alpamayo and one day resting there to allow some acclimatization to the new altitude (4,600m). So you'd be going for the summit, at best, on day 6. You'd be hard-pressed to squeeze in H. Potosi in the remaining time.

Forget about Peru. There is very little chance of getting anything good done in only 9-10 days. You would need to go to Huaraz, then spend at least 3 nights in Huaraz, then hike in to a BC such as Ishinca, spend at least one night there to acclimatize, and then you would finally be able to climb something moderate in altitude like Urus or Ishinca, neither of which is as interesting as Cotopaxi or H. Potosi. You wouldn't have any time left after that for anything else...maybe Tocllaraju if you were really lucky.

But...why not go someplace locally and get a ton of good climbing in...like the Sierras or the Tetons? A 9-10 day trip to S. America really isn't that practical in my opinion.

"Go to peru, it is cheaper and, at preent, lacks the political instability (although that may change). "

When I was there two years ago, Bolivia was very much cheaper than Peru. It was on the order of 2-3 soles to the dollar in Peru, and 8-10 Bolivianos to the dollar. Even in La Paz (you know, the big city) it was cheaper than, say Cusco or Puno. We also did H. Potosi in pretty much a weekend trip from La Paz. Illimani is doable in similar, but longer fashion. I haven't been to Quito, so what Tom says may trump my advice. I thought Bolivia was a cheap and easy way to climb altitude.

The style of climbing in Ecuador is very similar to the climbing in Mexico, but with more interesting glaciers and at slightly higher altitude. You can drive from Quito directly to the huts (in most cases) and then it's a day to the summit. Bolivia is also fairly convenient, but with a few more logistical issues. Both P. Alpamayo and H. Potosi have 3-4 hour approaches to base camp and you'll want mules or porters. I think that trying to go in to two different areas in just 9-10 days is pushing it. It's true that many of the peaks can be done in weekend trips from La Paz, but that usually only happens in reality after a good bit of acclimatization.

The Cabeza is a magnificent climb! Ala Izquierda, too. And there is also Pyramide Blanca, which has moderate routes on it from the Condoriri base camp. But i agree with Tom, your acclimatization will dictate how much climbing you can get done in such a short time. Some people have an easier time with it and can just jump right in. All of the climbing I did was after two weeks of touring in southern Peru, so I was well adjusted. We did have logistical problems in La Paz with every other day being a national holiday with roads blocked by parades and everthing closed.

Bird: I haven't been to Bolivia...yet...but I have memorized the guidebook. The guy I was climbing with this season in Peru was there for a month before we met up, so I got lots of info from him and saw his pics. He said that the weather was perfect every day for the entire month. That is definitely not the case in Ecuador, at least in Dec-Jan. He also said that conditions have changed quite a lot there and the guidebook is no longer very accurate. For example, he said that there was practically no snow on Cabeza de Condor...in June! I think you can't really go wrong with either Ecuador or Bolivia, but if you really want to go over 6000m, maybe Bolivia is the place.

There is definitely less snow on the Cabeza than in Yossi's guide. In fact, the directissima was a rock route when we were there, two years ago in June. The route was mostly neve and ice. Take screws, a full rack (4-6) for the last couple of pitches. The weather was immaculate the entire time. There were low clouds one morning, but mostly fog rolling in from the jungle to the east. If everything went perfect, you could bag Pequeno Alpamayo and the Cabeza from La Paz in 10 days. But that doesn't leave much room for error. You would likely get one or the other at least. In my opinion, Peq. Alpamayo was a good warm up route, but the Cabeza was the goods. We used Adolfo Andino outfitters (right on Sagarnaga, next to Hotel Sagarnaga) for rides and they also worked out mules from Tumi to basecamp. The hike to basecamp is mellow, but if you aren't acclimated, it might be brutal to hike in all of your stuff. Basecamp is at about 15k. And I think the Cabeza is like 18.6k feet. The trips we looked at for Hyuana Potosi and Illimani were 3-5 days round trip from La Paz. So you could spend a few days lounging in town at 12k and make an attempt on one of those right at the end of the trip. There is sick mountain biking right outside of town with huge descents, and some pretty cool scenery to check out while you get situated to the altitude. La Paz is a funky city, kind of cool. Good Luck!

I was on Huayna Potosi and Pequeno Alpamayo two seasons ago. Unbelievable. Both are fabulous climbs with interesting terrain - much more than cotopaxi-type glacier cimbs. Basecamps are within a couple of hours of La Paz by car. Weather was immaculate in late June. It's a great trip. I throw my hat in that ring.

Maybe this will help you to make a decision:
I have just came back from a 3-week trip to Bolivia visiting my in-laws in La Paz. I spent 6 days in the Condoriri base camp, from Aug. 11 to Aug. 16, and climbed the direct face of Peq. Alpamayo as a warm-up, then "Normal" (non-face, as face is all rock) route on Cabeza, and finally the "British route" on Huallomen. The first two routes had perfect neve on them, the third one, usually a mixed ice climb, had rather little ice, requiring more rock protection and rock-climbing than usual. This season, according to local guides, is considered rather dry.

On the last day we got dumped by a foot of snow. Generally, weather in Bolivia is very stable, however in August there is a chance of snowstorm, usually closer to the end of the month. The snowstorm of 16-th was considered by local an anomaly. Before the storm, the pattern was to have clearing during the night, good weather until 1pm, then fog/clouds rolling over, maybe with some little precipitation between 3pm and 6pm, then picking up winds and clearing through the night.

On political situation: nothing indicating instability similar to 2004/2005 is happening at the moment, so this would not be your worry.

Looks like you've already decided but I'd like to add my voice to the others saying Bolivia's the place to be. I've climbed in both countries and found the climbing in Bolivia far superior for a number of reasons, many of which have been already mentioned here. The elevations of the peaks are higher (although you can't generally get the cheap elevation you can in Ecuador), the weather's historically better (especially for your time frame), and you're in actual mountain ranges, cirques, etc., instead of hitting mostly isolated volcanoes. At Condoriri alone you can ccamp and climb something like 14 different peaks from the same camp.

However, as others have mentioned, unless you live at a high elevation or can go to one just before your trip for a couple of weeks, acclimitization might be a problem. I'd think you might want at least 2 weeks at decent altitude before trying something over 6000m, although you could get lucky I suppose. Good climbing....